1. Field of the Invention
The present invention relates to the manufacture of electrical circuitry and more particularly concerns the method of attaining a corrosion resistant barrier upon isolated areas of electrical circuitry by employing a reusable mandrel.
2. Description of Related Art
Many different types of printed circuits employ gold or other corrosive resistant coatings on exposed conductive surfaces, among such circuits are those having projecting connective elements. Such connective elements are used in printed circuits that are connected to one another by projecting elements in the form of metallic interconnection features that are pressed against similar projecting features or mating metallic connecting pads on the other circuit components. Flexible circuit terminations and connecting wafers of this type are described in U.S. Pat. No. 4,125,310 to Patrick A. Reardon II, U.S. Pat. No. 4,116,517 to Selvin et al. and U.S. Pat. No. 4,453,795 to Moulin. For, many applications, whether or not projecting connective features are used it is required that exposed circuitry and, particularly the raised connection features on the circuitry be coated with a corrosion resistant material such as gold. Electroless gold plating results in a porous surface that is incapable of providing effective corrosion resistance. Additionally, the purity of the gold is inferior to electrodeposited gold due to the co-deposition of the reducing agent in the electroless solution. Accordingly, electrodeposition is employed to achieve non-porous corrosion barriers. To electroplate a raised feature an electrical connection is made to the feature, frequently by means of a lead that extends to the edge of the circuit part where plating current is provided. However, in some instances the circuit is isolated, that is, it has no electrical connection to edges of the part on which it is mounted. Accordingly, it is common, when corrosion plating isolated raised features, to form an additional conductive path from the feature to the periphery of the part to provide a path to be used solely for electroplating current. Once the gold plating is completed, this conductive path has no use. Nevertheless, after cutting the part to final dimensions, this conductive plating path remains and provides a path for possible future shorting because it forms a bare lead at the edge of the product. Another disadvantage of the use of these conductive plating paths is the fact that they require area on the surface of the part which may be more efficiently used for functional circuit traces.
Accordingly, it is an object of the present invention to provide a corrosion resistant coating on an isolated circuit in a manner that minimizes or avoids problems of the prior art.